In the technical field, recently, it has become more and more important to provide a wideband radio access scheme where high-speed and high-capacity communications are effectively performed. To that end, a multi-carrier system, more specifically, an Orthogonal Frequency Division Multiplexing (OFDM) system is expected to be used in downlink transmission from a viewpoint that high-speed and high-capacity communication may be performed while multi-path fading may be effectively reduced. Further, for a next-generation system, a frequency scheduling scheme is also being proposed from a viewpoint of enhancing efficiency of frequency use and throughput.
As shown in FIG. 1, a frequency band usable in a system may be divided into plural resource blocks (divided into three in the example of FIG. 1), and each resource block includes one or more sub-carriers. The resource block may be also called a “frequency chunk”, and one or more resource blocks are allocated to a terminal. In the frequency scheduling, the resource blocks may be preferentially allocated to a terminal having good channel quality in accordance with the received signal quality or a Channel Quality Indicator (CQI) with respect to each resource block of the downlink pilot channel (PICH) reported from each terminal. By doing this, the transmission efficiency and the throughput of the total system are intended to be improved. In a case where the frequency scheduling is preformed, it is necessary to notify the content of the scheduling to the terminal. The content is transmitted through a control channel (CCH) (or may be called an L1/L2 control signaling channel or an associated control channel). In addition, through the control channel (CCH), a modulation method to be used in scheduled resource blocks (such as QPSK, 16QAM, and 64QAM), channel coding information (such as a channel coding rate), and a Hybrid Auto Repeat ReQuest (HARQ) scheme are also transmitted. The technique of dividing a frequency band into plural resource blocks and selecting a modulation method for each resource block is described in, for example, Non Patent Document 1.
Non Patent Document 1: P. Chow, J. Cioffi, J. Bingham, “A Practical Discrete Multitone Transceiver Loading Algorithm for Data Transmission over Spectrally Shaped Channel”, IEEE Trans. Commun. vol. 43, No. 2/3/4, February/March/April 1995.